The game no longer has this problem for me, it must be something related to transform feedback or with nVidia drivers. The game works like native for me.
Distro:Antergos Linux
Kernel:4.19.4-arch1-1-ARCH
RAM:16 GB
GPU Driver:NVIDIA 415.22
GPU:NVIDIA GeForce GTX 1070
CPU:Intel Core i5-6600K @ 3.50GHz
Great, I haven't played it for a long time and even uninstalled but might return back. Thanks!
Can confirm, the terrain renders correctly now as of driver v410.78 and Proton 3.16-5 Beta.
proton 3.16-5x1 2018-12
In the very first mission, "Short-Fused" the terrain almost always is not rendered appearing only in certain locations on the map. Other than that the game is fully playable and has great framerates.
My specs: Intel Core i7-7700k, 32Gb RAM, NVIDIA GeForce 1070 GTX driver v396.54, Debian Buster GNU/Linux amd64, Awesome WM 3.5.6, kernel v4.17.12